Spot welding cap changer

ABSTRACT

The invention relates to a spot welding cap changer ( 1 ) with a cap puller ( 2 ) and two cap magazines ( 3, 3 A), the cap puller ( 2 ) having a gripper ( 20 ) with spring-loaded, pivotable jaws ( 21, 22 ), which in response to a turning and axial pulling-off movement detaches a spot welding cap (K) of a pincer spot welding head introduced into it from a shaft of the pincer welding head in such a way that it is clamped to prevent it twisting, and the cap magazines ( 3, 3 A) holding spot welding caps respectively in a round cap carrier ( 31 ) such that they are circularly arranged in a directed and oriented manner and are respectively transported individually one after the other into an access position against a stop ( 32 ) by an advancing force (P).

This application is a continuation of application Ser. No. 11/997,131,filed on Jul. 30, 2008, now U.S. Pat. No. 8,314,356.

The invention relates to a spot welding cap changer with a cap extractorand two cap magazines, the cap extractor having a gripper withspring-loaded, pivoting jaws, which in response to a turning and axialextraction movement detaches a spot welding cap of a pincer spot weldinghead inserted into it from a shaft of the pincer welding head in such away that it is clamped to prevent twisting, and the cap magazinesholding spot-welding caps in a cap carrier in such a way that they arecircularly arranged in a directed and oriented manner and are one by onetransported by an advancing force against a stop, into an accessposition allowing to attach them axially to the free shaft of the pincerand to extract them with it.

Such a mechanical electrode cap changer is known from the DE 102 22 248A1. It has a two-part cap extractor, accessible from both sides, in abody separate from the magazine.

Since gravity causes the caps to slide against a cap stop, the devicecan only be operated stationary in the vicinity of a mobile weldingrobot. Changing caps at a stationary pincer spot welding head, to whicheach component is fed by a robot for welding, is therefore not possible.The pincer spot welding heads/welding installations often have shortshafts, which are for instance curved, so that the cap extractor,equipped with three large jaws and accordingly big, cannot be positionedfor extraction.

It is the object of the invention to provide for an automatic faster andsafer exchange of the spot welding caps both at mobile and stationaryspot welding installations with a short access distance.

The solution resides in that the cap extractor has two opposed grippers,each with jaws that are open at their ends and can be rotated towardseach other with approximately parallel toothed grip surfaces whosedistance is slightly smaller than a diameter of a spot welding cap, andeach cap magazine contains a cap carrier, which, driven by a spring box,presses by way of its advancing force one of the caps respectivelyagainst the stop, and in the access position a rim overlap overlaps thecap on one side.

Advantageous forms of the invention are indicated in the subclaims.

In the new embodiment the cap extractor and the magazine are mounted ona support which preferably is spring-mounted. In contrast to the knownsystem, the new construction design gives the possibility not only to beused at welding robots, but also at stationary pincer welding heads orwelding installations.

Compared with the known clamping system with three jaws, the newcap-extraction installation provides for shorter clamp and spin travels,therefore much shorter intervals for detaching the caps. Moreover, fromthe smaller design results a wider array of application, for instance atnon-standard pincers or very short, curved shafts.

The two cap extractors are each open at the ends of the jaws and thusaccessible to a cap. The jaws grip it directly by way of the undersizeof their distance and detach the cap, whereby a rotation around an angleof about 30-60° suffices. This way a cap change is possible even inextremely narrow confines. Since the two grippers are oriented inopposite directions, respectively one of them is accessible from thevarious sides in a clockwise rotation, so that no turning of the pinceris necessary, even if the pincer shafts are screwed on.

Furthermore, the round magazine is much more compact than the straightmagazine functioning by gravity of the known installation. It can beheld and operated in any position because of the spring drive.

Furthermore, the two round magazines arranged on parallel axes providein each case for an access with short radial travel to the accesspositions in the access openings. In an embodiment with a magazinecover, this cover is directly shifted during access, far enough to letthe rim overlap uncover the cap frame, so that the detaching ispossible. The example shows a radial infeed and an axial access of theshafts into the magazine.

Both partial devices, the cap changer, and the cap magazine, are mountedon a support close to one another, and thus can be set up stationary, ormounted to a robot arm in a fixed or detachable manner. In the firstcase the welding robot changes the caps of its own pincer, and in thesecond case the robot changes the caps at the stationary pincers orinstallations respectively by means of the device. The changing deviceat the robot arm is movably mounted, constantly ready for operation in afree space next to the gripper of the robot or on a guide rail, or it islocated in a parking position, where it can be picked up and brought tooperation by the gripper; this is called alternating pincer principle.

Advantageously, cap sensors are arranged on the device, which indicatewhether a cap is in place or not. Moreover, the charging level of themagazines is monitored. This way it is ensured that after a cap change acap is in place at the shaft of the pincer welding head before thecooling water is switched on. Furthermore it can be verified, whetherthe old cap was removed, when it is reported that there is no cap inplace while the shaft is approaching.

The embodiment of the cap magazine without a cover holds the weldingcaps in an elastic cap carrier in a close fit, axially movable bypropulsive or tractive force.

Advantageous embodiments are represented in the FIGS. 1 to 6.

FIG. 1 shows the entire device schematically and in perspective;

FIG. 2 shows a transparent top view of the cap extractor;

FIG. 2A, 2B show detailed enlargements of the grip surfaces;

FIG. 3 shows a perspective of the cap extractor;

FIG. 4 shows a cap magazine in perspective, closed, enlarged;

FIG. 5 shows a cap magazine in perspective, open, enlarged;

FIG. 6 shows a top view of the magazine cover.

FIG. 1 shows a complete spot welding cap changer 1, which is movablyheld on a support rail 5 at a robot arm. Alternatively, it is firmlymounted with the mounting plate 50. The bilaterally equipped capextractor 2 is bolted at the free end of the mounting plate 50, with thetwo grippers 20 respectively on the sides, their direction opposite toone another. Pulled off caps K are depicted between the jaws 21, 22,after being detached at the rim of a storage container they drop intoit.

Offset to the rear from the cap extractor 2 respectively one capmagazine 3, 3A laterally offset to the other is mounted on the mountingplate 50, with the magazine cover 4 respectively directed laterally andthe access openings 40 oriented axially parallel to the extractedwelding caps K that are still held by the gripper, so that the shafts ofthe pincer spot welding head have to travel only short distances whilechanging the caps.

FIG. 2 shows a top view on the cap extractor 2, which consists of veryfew parts. The grippers 20 are composed of one fixed, toothed jaw 21respectively, and one jaw 22 which is mounted in such a way that it canbe pivoted towards said jaw 21. The pivot joint 24 is located behind thefixed jaw 21 by way of a U-shaped structure of the movable jaw arm 25,so that a cap K positioned in the gripper 20 will be clamped at a twistdepending on the direction of rotation.

The initial pressing force of the jaws 21, 22 is caused by a bracingspring 26, which for example, is formed as a spiral or bracing springwith spread ends, each pressing against a jaw arm 25.

On the infeed side the grippers 20 are provided with infeed skews 27,28. From these extend the roughly parallel grip surfaces 23, each with atoothing in opposite direction 29A, 29B, as FIGS. 2A and 2B show inpartial view and in detail. If there is no cap K inserted in thegrippers 20, then the distance A of the grip surfaces 23 has a minorundersize compared to the cap outside diameter D.

FIG. 3 shows that the spring 26 and the movable jaws 21, 22 as well as ajaw plate 62, on which the fixed jaws 21 are formed, are held betweentwo cover plates 60, 61. The jaw plate 62 has a corresponding cavity, inwhich the U-shaped jaw arms 22 have free space to move.

FIG. 4 shows a round cap magazine 3, which consists of a barrel shapedcap carrier 31, closed with a magazine cover 4, whereas a radial sectionremains free up to the rounded access opening 40, in which a welding capK in the withdrawal position is pressed to the edge of a stop 32 at thecover.

The cover 4 has a small rim overlap 41 of the cap frame in the curve ofthe access opening 40, an induct skew 42 connecting to said rim overlapwhich is cascaded to the top side of the cover. At an embodiment with ahinged cover 4, a slot 43 is formed, through which reaches a bracket 34,bevelled on the outside, which keeps the cover shut.

On the other side of the access opening 40 a hinge 44 with a slottedhole 45 is formed in the extension level of the cover, the cones 46 ofsaid hinge being held in a hinge support 47.

FIG. 5 shows the open round magazine 3 with a hinge and equipped with awelding cap K in the drill holes 30 of the cap carrier 31, the cap Kprotruding by a few millimeters. A firmly mounted spring box 33,schematically depicted, is in the centre of the cap carrier 31, saidspring box carrying the bracket 34 so that it can be radially moved. Apreloaded spindle or spiral spring is arranged centrally in the springbox 33, one end of the spring being fixed to the spring box 33, theother to the cap carrier 31, so that the latter is pressed with atorsion force P in the direction of the stop 32, which extends radiallyon the magazine cover.

The plate-shape bracket 34 extends in a diagonal guiding slot on thecover of the spring box 33. In the closed state, as shown here, acompression spring arrangement 35, held in the cover, extends from thebracket 34 and is supported by means of a support pin 36 on the roundedhinge support 47, and presses the bracket 34 in the closed position, inwhich it overlaps the cover 4 in the closed state and holds the rimoverlap 41 in the overlap position, the cone 46 being in the rear stopposition in the slotted hole 45, as FIG. 1 shows. To open the cover 4,the bracket 34 is pushed back manually. Alternatively, the roundmagazine can be implemented without a hinge for the opening of thecover. In this case the cover is only held in a movable manner, so thatthe shaft of the pincer, when inserted, slides the cover by the skew 42to release the rim overlap.

FIG. 6 shows a top view on the magazine cover 4, whose main outlineconsists of two semi-circles with shifted centres M1, M2, whereby on oneside the access opening 40 extends in the direction of the centre, andon the opposite side the hinge 44 extends on the outside. The slot inthe cover 43 extends 4 in the central area in the direction between theaccess opening 40 and the hinge 44. The bracket 34 in the cover and inthe fixed spring box 33 is guided in this direction. The cover 4 isabout 15 mm high and largely hollow shaped and has a stiffening coverrim 48, which passes into the stop 32 and on the other side into thehinge 44. The cover 4 is lowered at the induct skew 42 by about 5 mm tothe infeed area. Internally, the cover surface drives the caps to thewithdrawal level when turned in the stop position. A chamber 49, whichcontains the compression spring arrangement 35, is represented with adashed outline.

The compact construction of the cap extractor with the magazines allowsfor a significant reduction of the changing times, for example, from 22to 17 sec, which corresponds to about 23%.

LIST OF REFERENCE SIGNS

-   1 spot welding cap changer-   2 cap extractor-   20 gripper-   21, 22 jaws-   23 grip surfaces-   24 pivot joint-   25 jaw arm-   26 bracing spring-   27, 28 infeed skews-   29A, 29B toothing-   3, 3A cap magazine-   30 drill holes-   31 cap carriers-   32 stop-   33 spring box-   34 bracket-   35 compression spring-   36 support pin-   4 magazine cover-   40 access opening-   41 rim overlap-   42 induct skew on the cover-   43 slot in the cover-   44 hinge-   45 slotted hole in the hinge-   46 cones-   47 hinge support-   48 cover rim-   49 compression spring chamber-   5 support rail-   50 mounting plates-   60, 61 cover plates-   62 jaw plate-   A gripping jaw distance-   D outside diameter of the caps-   K cap-   P advancing force-   M1, M2 semicircle centres

The invention claimed is:
 1. Spot welding cap changer comprising: a capextractor and two cap magazines, the cap extractor having: a gripperwith spring-loaded, pivoting jaws which in response to a turning andaxial extraction movement detaches a spot welding cap of a pincer spotwelding head inserted into the pivoting jaws from a shaft of the pincerwelding head in such a way that the spot welding cap is clamped toprevent the spot welding cap from twisting, and the cap magazinesholding spot welding caps respectively in a cap carrier in such a waythat the spot welding caps are circularly arranged in a directed andoriented manner and are one by one transported by an advancing forceagainst a stop, into an access position allowing the spot welding capsto be attached axially to the free shaft of the pincer and to extractthem with the free shaft of the pincer, wherein the cap extractor hastwo opposed grippers, each with jaws that are open at their ends and canbe rotated towards each other with approximately parallel toothed gripsurfaces whose distance is smaller than a diameter of a spot weldingcap, and each cap magazine has a cap carrier which, driven by a springbox, presses by way an advancing force one of the caps respectivelyagainst the stop.
 2. Spot welding cap changer according to claim 1,wherein respectively one of the jaws of the corresponding gripper isfixed at a jaw plate, and the corresponding movable jaw is formed at anU-shaped jaw arm, which is supported with a pivot joint behind the fixedjaw.
 3. Spot welding cap changer according to claim 2, wherein betweenthe two movable jaw arms, a preloaded bracing spring is mounted.
 4. Spotwelding cap changer according to claim 1, wherein the jaws have infeedskews.
 5. Spot welding cap changer according to claim 4, wherein thegrip surfaces in each case have an asymmetric toothing, which on the twoparallel jaws is oriented in opposite directions.
 6. Spot welding capchanger according to claim 3, wherein the jaw arms, the bracing springand the jaw plate are held between cover plates.
 7. Spot welding capchanger according to claim 1, wherein the spring box contains a spiralor coil spring, one end of which is fixed at the spring box, and theother end of which is fixed at the cap carrier.
 8. Spot welding capchanger according to claim 1, wherein a magazine cover is held preloadedby a spring in the direction of the access opening so that the rimoverlap overlaps a cap frame in a stop position of the magazine cover.9. Spot welding cap changer according to claim 8, wherein a bracket isspring-loaded and movably held at the spring box, said bracket reachingthrough the closed magazine cover and, by overlapping the magazinecover, holding the magazine cover in place.
 10. Spot welding cap changeraccording to claim 8, wherein the magazine cover is articulated at ahinge support, situated opposite of the access opening.
 11. Spot weldingcap changer according to claim 10, wherein the magazine cover is movablyguided in a slotted hole on the hinge support.
 12. Spot welding capchanger according to claim 1, wherein the magazine cover bears astiffening cover rim, which on one side forms the rim overlap and on theother side forms a hinge.
 13. Spot welding cap changer according toclaim 1, wherein the cap extractor with grippers is mounted on amounting plate, on which with an offset to the rear the cap magazinesare mounted.
 14. Spot welding cap changer according to claim 13, whereinthe access openings of the cap magazines are directed towards andsalient on different sides of the mounting plate, respectively.
 15. Spotwelding cap changer according to claim 13, wherein the mounting plate issupported and movably guided on a support rail which is mounted on arobot arm or firmly installed.
 16. Spot welding cap changer according toclaim 1, wherein sensors are arranged at the cap magazines, which send asignal to a control device when a predetermined remaining quantity ofspot welding caps is in stock in the respective cap carrier.
 17. Spotwelding cap changer according to claim 1, wherein the magazine coverbears a stiffening cover rim.
 18. Spot welding cap changer according toclaim 1, wherein the cap extractor is mounted on a mounting plate. 19.Spot welding cap changer according to claim 9, wherein the magazinecover is articulated at a hinge support.
 20. Spot welding cap changeraccording to claim 13, wherein the mounting plate is supported on asupport rail.
 21. A cap magazine for use with a cap extractor thatdetaches a spot welding cap of a pincer spot welding head inserted intothe cap extractor from a shaft of the pincer welding head, the capmagazine comprising: a cap carrier sized and shaped to receive aplurality of spot welding caps in a circular arrangement; and a springbox for driving the spot welding caps within the cap carrier, the springbox providing an advancing force to advance the caps one by one so thatone of the caps bears against a stop in the cap magazine in an accessposition, the access position allowing the spot welding caps to beattached axially to the free shaft of the pincer welding head and to beextracted from the cap carrier with the free shaft of the pincer, andwhen the cap in the access position is extracted from the cap carrier,the spring box advances another cap into the access position.
 22. Thecap magazine of claim 21, wherein the spring box includes a spring, oneend of which is fixed at the spring box, and the other end of which isfixed at the cap carrier.
 23. The cap magazine of claim 21, wherein amagazine cover is held preloaded by a spring in the direction of theaccess opening so that the rim overlap overlaps a cap frame in a stopposition of the magazine cover.
 24. The cap magazine of claim 23,wherein a bracket is spring-loaded and movably held at the spring box,said bracket reaching through the closed magazine cover and, byoverlapping the magazine cover, holding the magazine cover in place. 25.The cap magazine of claim 23, wherein the magazine cover is articulatedat a hinge support, situated opposite of the access opening.
 26. Spotwelding cap changer according to claim 1, wherein in the accessposition, a rim overlap overlaps the cap on one side.
 27. The capmagazine of claim 21, further comprising a rim overlap that overlaps thecap in the access position on one side.